JPH0688187A - Production of alloyed galvannealed steel sheet - Google Patents

Abstract

PURPOSE:To provide a method capable of forming an alloyed galvannealed layer free from the generation of nonplating and the nonuniformity in alloying and excellent in uniformity and powdering resistance on the surface of a steel sheet contg. elements oxidizable more easily than Fe or elements having a surface concentrating tendency at the time of annealing. CONSTITUTION:Before the immersion of an annealed steel sheet into a galvanizing bath 12, a metal covering layer having 0.1 to 3.0mum thickness constituted of at least one selected from a group consisting of Fe, Ni, Co and Cu is formed on the surface of the steel sheet 2, and the steel sheet in which the metal covering layer has been formed is subjected to galvanizing treatment and is then subjected to alloying treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention is applied to Si, Mn, P, Cu, Ni,
For forming a uniform galvannealed layer on the surface of a steel sheet containing an element that is more easily oxidized than Fe during annealing or has a strong surface concentration tendency, such as Cr.
The present invention relates to a method for manufacturing a galvannealed steel sheet.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of preventing global warming, it has been required to improve the fuel efficiency of automobiles.
There is a demand for reducing the weight of automobile bodies, that is, reducing the thickness of steel sheets for automobile bodies. On the other hand, from the viewpoint of ensuring the safety of the automobile body, higher strength of the steel sheet for automobile body is required. Since the galvannealed steel sheet is excellent in corrosion resistance and electrodeposition coating property, it has been widely used as a steel sheet for automobile bodies from the past, but it satisfies the requirements for thinning and high strength of the above-mentioned steel sheet. Therefore, the development of an alloyed hot-dip galvanized steel sheet in which an alloyed hot-dip galvanized layer is formed on the surface of a high-strength steel sheet is under way. On the other hand, in order to further improve the corrosion resistance, development of an alloyed hot-dip galvanized steel sheet in which an alloyed hot-dip galvanized layer is formed on the surface of a steel sheet having excellent corrosion resistance is under way.

The production of the galvannealed steel sheet is carried out by continuously passing the steel sheet through a continuous hot-dip galvanizing line facility and using the same facility as follows. That is, the steel sheet is continuously annealed, and then the annealed steel sheet is continuously passed through a galvanizing bath, and the steel sheet is subjected to a hot dip galvanizing treatment to form at least one surface of the steel sheet. Forming a hot-dip galvanized layer, then heating the steel sheet on which the hot-dip galvanized layer has been formed, subjected to an alloying treatment, thus on at least one surface of the steel sheet,
An alloyed hot-dip galvanized layer is formed.

Generally, in order to improve the strength of a steel sheet, it is practiced to add a solid solution strengthening element such as Si, Mn or P to the steel. On the other hand, in order to improve the corrosion resistance of the steel sheet, elements such as Cu, P, Cr and Ni are contained in the steel.

When an alloyed hot-dip galvanized layer is formed on the surface of a steel sheet containing elements such as Si, Mn, P, Cu, Cr and Ni described above in a continuous hot-dip galvanizing line facility, annealing in the line In the process, Si, Mn, P, Cu, Cr, Ni in steel
And other elements are concentrated in the surface layer of the steel sheet, or oxides of the above elements are generated on the surface of the steel sheet, resulting in non-plating or uneven alloying of the plating layer, resulting in uneven plating layer and powdering resistance. Defects such as deterioration occur. In addition, similar defects occur due to nonuniformity of the steel sheet surface before hot rolling.

[0006] Many studies have been made in the past for solving the above-mentioned problems and for preventing the influence of the element concentrated on the surface layer of the steel sheet in the annealing step. For example, the following method has been disclosed. There is. A method disclosed in Japanese Examined Patent Publication No. 55-44151: consisting of forming a copper plating layer on the surface of the steel sheet before annealing the steel sheet, then annealing the steel sheet on which the copper plating layer is formed, and then hot dip zinc Plating (hereinafter referred to as Prior Art 1). A method disclosed in Japanese Examined Patent Publication No. 60-56418, which comprises: forming an iron plating layer on the surface of the steel sheet before annealing the steel sheet; and then applying H ₂ gas to the steel sheet on which the iron plating layer is formed. It is annealed in a reducing atmosphere containing it and then hot-dip galvanized (hereinafter referred to as prior art 2).

A method disclosed in Japanese Examined Patent Publication No. 61-9386, which consists of the following: before annealing the steel sheet,
A plating layer of Ni, Co or a NiCo alloy is formed, and then a steel sheet having such a plating layer is annealed in a reducing atmosphere containing hydrogen gas and then hot dip galvanized (hereinafter referred to as prior art 3). ). Japanese Unexamined Patent Publication No. 2-194156 discloses a method consisting of the following: Before annealing a steel sheet, a Fe-B alloy plating layer was formed on the surface of the steel sheet, and then a Fe-B alloy plating layer was formed. A steel sheet is hot dip galvanized (hereinafter referred to as Prior Art 4). Japanese Unexamined Patent Publication (Kokai) No. 4-28852, which comprises the following method: After reducing a steel sheet with a reducing gas, a metal is vapor-deposited on the surface of the steel sheet immediately before hot dip plating (hereinafter referred to as prior art 5). .

According to the prior arts 1 to 4, since the pre-plated layer of Fe, Ni, Cu, Co or the like is formed on the surface of the steel sheet before the annealing step, the heat generated on the surface of the steel sheet is The non-uniformity before rolling can be eliminated to some extent.

[0009]

However, the prior arts 1 to 4 have the following problems. Si, Mn, P, Cu, Cr, Ni in the steel during the annealing process
And other elements diffuse into the pre-plating layer and concentrate on the surface layer of the pre-plating layer, resulting in non-uniformity of the surface of the pre-plating layer, preventing non-plating and uneven alloying that occur in the galvannealed layer. Can not do it. The enrichment of the above elements depends on the annealing conditions and the component composition of the steel, and is particularly likely to occur when the annealing temperature is high or the soaking time is long.

In order to prevent unevenness from occurring on the surface of the pre-plated layer, it is necessary to form a large amount of the pre-plated layer on the surface of the steel sheet. As a result, a large-scale pre-plating equipment must be installed upstream of the annealing furnace, and thus a large amount of equipment cost is required.

As described above, in the annealing step, in order to prevent the elements such as Si, Mn, P, Cu, Cr and Ni in the steel from being concentrated on the surface of the pre-plating layer, the annealing condition is set. That is, the annealing temperature and soaking time must be controlled.
Further, as described in Prior Art 4, the plating amount of the pre-plating layer for improving the hot dip galvanizing property depends on the composition of the steel, for example, the content of Si or Cr in the steel. . Therefore, a uniform alloyed molten zinc is formed on the surface of the steel sheet containing elements such as Si, Mn, P, Cu, Ni, Cr, etc. that are more easily oxidized than Fe during annealing or have a strong surface concentration tendency. In order to form the plating layer, in addition to the operating conditions of the continuous hot-dip galvanizing that is usually performed, the plating amount of the pre-plating layer must be controlled according to the composition of the steel sheet to be plated and its annealing conditions. Therefore, the operation becomes very complicated and difficult.

Prior art 5 relates to the production of hot-dip galvanized steel sheets, not the production of alloyed hot-dip galvanized steel sheets as in the present invention.

Therefore, an object of the present invention is to solve the above-mentioned problems and to provide an element such as Si, Mn, P, Cu, Ni, Cr, etc., which is more likely to be oxidized than Fe during annealing or has a strong surface concentration tendency. On the surface of the steel sheet containing the element, when forming an alloyed hot-dip galvanized layer, non-plating, no uneven alloying, etc., an alloyed hot-dip galvanized layer excellent in uniformity and powdering resistance, To provide a method for producing an alloyed hot-dip galvanized steel sheet which can be easily and economically formed without installing a large-scale pre-plating facility and which has particularly high strength and excellent corrosion resistance. is there.

[0014]

From the above-mentioned viewpoint, the present inventors have found that, on the surface of a steel sheet containing an element that is more easily oxidized than Fe during annealing or an element that has a strong surface concentration tendency, unplating or alloying An alloyed hot-dip galvanized layer with excellent uniformity and powdering resistance without unevenness
In order to develop a method for forming easily and economically,
We have earnestly studied.

The inventors of the present invention firstly analyzed Si, Mn, P, Cu, Ni,
Alloying unevenness and non-plating that occur when forming an alloyed hot-dip galvanized layer on the surface of a steel sheet that contains elements such as Cr that are more likely to oxidize than Fe during annealing or have a strong surface concentration tendency. The shape and the cause of its occurrence were investigated in detail. As a result, the following was revealed.

Scaleable alloying unevenness: Scaleable alloying unevenness is an alloying abnormality (unevenness) having a width of about 1 cm,
Traces may remain even after painting, which is not desirable in appearance. Such scale alloy unevenness is generated on the surface of the slab during heating, resulting in partial formation of Si, Mn, P, Cu, Ni,
Low melting point complex oxide containing Cr, as a result of hot-rolling the slab and then remaining on the surface of the steel sheet after pickling, when subjected to hot dip galvanizing treatment on this steel sheet, the complex oxide of the steel sheet The abnormal alloying reaction occurs in the remaining portion of the alloy.

[0017] Selective oxidative alloying unevenness: Selective oxidative alloying unevenness is an alloying anomaly (unevenness) of about several hundreds of microns, and the plating amount locally increases (abnormal) in the alloyed hot-dip galvanized layer. Alloying) occurs and deteriorates the powdering resistance. Such alloying unevenness is caused by selective oxidation of Si, Mn, P, Cu, N formed on the surface of the steel sheet immediately before plating.
It is caused by the presence of the density of oxides containing i and Cr.

Alloying unevenness: Alloying unevenness is caused by Si, Mn,
It occurs when elements such as P, Cu, Ni, and Cr concentrate on the grain boundaries and the surface of the steel, and the alloying reaction rate slows during the alloying treatment after plating. Further, when the concentration of the above elements to the grain boundaries and the surface of the steel is significant, fine streak unevenness occurs on the surface of the steel sheet after the alloying treatment, and the surface appearance of the steel sheet is impaired, and the chemical conversion treatability And the paintability is adversely affected.

Non-plating: This is a missing portion of the plating layer that occurs in the hot-dip galvanized layer due to poor wettability between the hot-dip zinc and the steel sheet. Such non-plating is caused by Si, Mn, P,
The oxide containing Cu, Ni, Cr remains thickly on the surface of the steel sheet, and occurs when the molten zinc and the steel sheet do not react at all, that is, when they do not get wet.

As described above, Si, Mn, P, Cu, Ni, Cr
On the surface of the steel sheet containing elements such as, when forming the alloyed hot-dip galvanized layer, uneven alloying or non-plating that occurs in the plating layer, non-uniformity of the steel sheet surface before hot rolling, and,
This is due to the concentration and selective oxidation of the above components in the steel that occur during the annealing of the steel sheet, and is considered to occur due to the mechanism below.

Since the wettability between the steel sheet and the molten zinc at the moment when the steel sheet is immersed in the galvanizing bath is partially poor, non-plating and uneven alloying occur. The initial alloy layer formed at the moment when the steel sheet is immersed in the galvanizing bath changes due to the non-uniformity of the steel sheet surface, which adversely affects the subsequent alloying process, resulting in uneven alloying.

In view of the above, at least one surface of the annealed steel sheet is obtained by coating at least one surface of the steel sheet with a specific metal after passing through the galvanizing bath after annealing the steel sheet. If a metal coating layer with a thickness of 0.01 to 3.0 μm is formed on the steel sheet, and the steel sheet with such a metal coating layer is subjected to hot dip galvanizing treatment and then alloying treatment, the steel sheet is , P, Cu, Ni, Cr, etc., even if it contains an element that is more likely to oxidize than Fe during annealing or has a strong surface concentration tendency, non-plating, uneven alloying, etc. on the surface of the steel sheet It has been found that an alloyed hot-dip galvanized layer excellent in uniformity and powdering resistance can be easily and economically formed without causing the phenomenon.

The present invention has been made based on the above findings, in which a steel sheet is annealed continuously, and then the annealed steel sheet is continuously passed through a galvanizing bath,
The steel sheet is subjected to a hot dip galvanizing treatment to form a hot dip galvanized layer on at least one surface of the steel sheet, and then the steel sheet having the hot dip galvanized layer formed thereon is heated to undergo an alloying treatment. Thus, in the method for producing an alloyed hot-dip galvanized steel sheet, which comprises forming an alloyed hot-dip galvanized layer on at least one surface of the steel sheet, before passing the annealed steel sheet into the galvanizing bath. On at least one surface of the steel sheet, Fe, Ni,
One metal selected from the group consisting of Co and Cu or 2
A metal coating layer having a thickness of 0.01 to 3.0 μm on at least one surface of the annealed steel sheet coated with an alloy of at least one kind, and a steel sheet having such a metal coating layer formed thereon, It is characterized in that hot-dip galvanizing treatment is performed in a galvanizing bath containing 0.05 to 0.20 wt.% Al, and then alloying treatment is performed.

[0024]

According to the present invention, one or more metals selected from the group consisting of Fe, Ni, Co and Cu are provided on at least one surface of the annealed steel sheet before passing through the galvanizing bath. Since the metal coating layer made of two or more alloys is formed, the surface of the steel sheet is smoothed by the metal coating layer. Therefore, when the steel sheet is subjected to the hot dip galvanizing treatment, the wettability between the steel sheet and the plating bath at the moment when the steel sheet is immersed in the galvanizing bath becomes good. The alloying unevenness does not occur.

Further, since the surface of the steel sheet is smoothed by the metal coating layer, the initial alloy layer is uniformly formed on the surface of the steel sheet at the moment when the steel sheet is immersed in the zinc plating bath. The alloying process also becomes uniform. Therefore, alloying unevenness does not occur in the galvannealed layer.

As described above, the improvement of the wettability between the steel sheet and the plating bath and the uniform formation of the initial alloy layer in order to prevent the occurrence of non-plating and uneven alloying are caused by at least one of the annealed steel sheets. This can be done by forming a certain amount of metal coating layer on the surface. Therefore, it is not necessary to control the coating amount of the metal coating layer according to the component composition and annealing conditions of the steel plate to be plated, and the thickness of the coating layer is 0.
It can be extremely thin from 01 to 3.0 μm. Therefore, the operation is simple and easy and does not require the installation of large scale pre-plating equipment.

In the present invention, the metal of the metal coating layer formed on at least one surface of the annealed steel plate is
It must have a higher melting point than zinc and have good wettability with zinc. From this point of view, the above metals are replaced by Fe, N
It is limited to one metal or two or more alloys selected from the group consisting of i, Co and Cu. The thickness of the metal coating layer is 0.
It must be in the range of 01 to 3.0 μm. If the thickness of the coating layer is less than 0.01 μm, the surface of the steel sheet cannot be coated uniformly. On the other hand, if the thickness exceeds 3.0 μm,
The effect is saturated and becomes uneconomical.

The means for forming the metal coating layer on the surface of the steel sheet is a vapor deposition method, a sputtering method, a chemical vapor deposition method (CVD method).
Etc., any known means may be used. The formation of such a metal coating layer is performed in a continuous hot dip galvanizing facility between the annealing furnace and the hot dip galvanizing tank, for example, on the outlet side of a snout, a cooling furnace, a soaking furnace, or the like.

During galvanization, a galvanizing bath for performing hot dip galvanizing treatment on a steel sheet on which a metal coating layer is formed is used.
In order to suppress the formation of a brittle intermetallic compound of Fe and Zn, it is necessary to contain Al in an amount of 0.05 to 0.20 wt.%. If the Al content in the plating bath is less than 0.05 wt.%, The above-described effect of suppressing the formation of the Fe-Zn intermetallic compound cannot be obtained. On the other hand, when the Al content in the plating bath exceeds 0.20 wt.%, The above-described effect of suppressing the formation of the Fe-Zn intermetallic compound becomes too strong, resulting in a hindrance to the alloying treatment performed after plating.

In the present invention, the alloying treatment for the steel sheet on which the galvanized layer is formed is preferably performed by an induction heating type alloying furnace. The reason will be described below. Si, Mn, P, Cu, Cr, Ni in steel sheet
In the case where the content of the steel sheet is large, or the annealing conditions for the steel sheet are high temperature and long time, the surface of the steel sheet has non-uniformity before hot rolling, or Si, M
Concentration of components such as n, P, Cu, Cr, and Ni, and their oxides may be present in large amounts. Therefore, according to the method of the present invention, a metal coating layer is formed on the surface of the steel sheet after annealing, and then the steel sheet on which the metal coating layer is formed is subjected to hot dip galvanizing treatment and alloying treatment by a normal gas heating method. Even if it is applied, it may not be possible to prevent the occurrence of non-plating and uneven alloying.

However, when the alloying treatment is performed by the induction heating type alloying furnace, the surface of the steel sheet is preferentially heated, unlike the case where the alloying treatment is performed by the gas heating method. Therefore, by such heating, regardless of the non-uniformity of the steel sheet surface, because the reaction between iron and molten zinc in the surface layer of the steel sheet is forcedly generated, the non-uniformity before hot rolling present on the surface of the steel sheet, And S that occurs during annealing
The effects of the concentration of i, Mn, P, Cu, Cr, Ni, etc. and the presence of these oxides disappear.

The steel sheet on which the alloyed hot-dip galvanized layer is formed by the method of the present invention contains 50 wt.% Or more Fe on the alloyed hot-dip galvanized layer in an amount of 1 g / m ² or more. Fe
When the -Zn alloy electroplating layer is formed, it is possible to improve the sliding characteristics of the plated steel sheet between the plating layer and the press tool during press working, and the cratering resistance during coating.

The above sliding characteristics are related to the adhesiveness between the material on the surface layer of the coating and the tool, and the higher the melting point of the coating, the more
It is effective for improving sliding characteristics. The Fe content of the Fe-Zn alloy electroplating layer is defined to be 50 wt.% Or more because the melting point of the coating is increased and the sliding characteristics are improved. Fe-Zn alloy electroplated layer plating amount is 1 g / m ²
The above definition is because if it is less than 1 g / m ² , the Fe—Zn based alloy electroplating layer cannot be uniformly formed on the alloyed hot-dip galvanized layer. The upper limit of the plating amount of the Fe-Zn alloy electroplating layer is not particularly specified, but from the economical viewpoint, the upper limit is preferably 5 g / m ² .

As described above, when the alloying treatment for the steel sheet having the hot-dip galvanized layer is carried out by the induction heating type alloying furnace, the surface of the hot-dip galvanized layer is not oxidized. Fe-Zn alloy electroplating layer can be appropriately formed on the alloyed hot-dip galvanized layer, and compared with the case of alloying by gas heating,
It is possible to reduce the plating amount of the Fe-Zn alloy electroplating layer.

FIG. 1 is a schematic explanatory view showing a first embodiment of an apparatus for carrying out the method of the present invention. As shown in FIG. 1, a heating furnace 3 for annealing the steel sheet 2 along a moving path of the steel sheet 2 that is rewound by a rewinding machine 1 and moves toward a hot dip galvanizing tank 8 and a soaking furnace. 4 and the cooling furnace 5 are arranged in this order. Between the cooling furnace 5 and the hot dip galvanizing tank 8, there is a snout 7 for guiding the steel plate 2 cooled to a predetermined temperature by the cooling furnace 5 into the hot dip galvanizing tank 8 containing the galvanizing bath 12. It is provided.

Inside the hot dip galvanizing bath 8, there is disposed a sink roll 11 for reversing the moving direction of the steel sheet 2 guided into the galvanizing bath 8 upward. Above the hot dip galvanizing bath 8, a gas wiper 9 for controlling the amount of the galvanizing bath adhering to the surface of the steel plate 2 which moves close to the galvanizing bath 8 and moves substantially vertically upward. And an alloying furnace 10 is provided above the gas wiper 9.

In the snout 7, there is provided a metal coating device 6 for forming a metal coating layer of a predetermined thickness on at least one surface of the steel plate 2 by the method of the present invention. In FIG. 1, the heating furnace 3, the soaking furnace 4, and the cooling furnace 5 are arranged substantially horizontally toward the hot dip galvanizing tank 8, and the steel plate 2 horizontally moves in each of the above-mentioned furnaces. Although it is of a furnace type, the heating furnace 3, the soaking furnace 4 and the cooling furnace 5 are arranged substantially vertically toward the hot dip galvanizing tank 8, and the so-called steel plate 2 moves vertically in each furnace. It may be a vertical furnace type.

The steel sheet 2 rewound by the rewinding machine 1 and moving toward the hot dip galvanizing tank 8 is heated to a predetermined temperature while being moved through the heating furnace 3, the soaking furnace 4 and the cooling furnace 5. Annealed after soaking and cooling. The steel sheet 2 thus annealed is introduced into the hot dip galvanizing tank 8 through the snout 7, and immediately before that, at least one of the steel sheets 2 is provided by the metal coating device 6 provided in the snout 7. On the surface, one metal or two or more alloys selected from the group consisting of Fe, Ni, Co and Cu, 0.
A metallization layer with a thickness of 01 to 3.0 μm is formed.

In this way, the steel sheet 2 on which the metal coating layer is formed is introduced into the hot dip galvanizing tank 8 and the plating layer 8 is formed.
The sink roll 11 in the inside moves upward substantially vertically and pulls it out of the plating layer 8. The steel sheet 2 drawn out from the plating layer 8 is heated in the alloying furnace 10 after the amount of zinc deposited on the surface thereof is adjusted by the gas wiper 9, and thus the hot dip galvannealing layer is formed on the surface of the steel sheet 2. It is formed.

FIG. 2 is a schematic explanatory view showing a second embodiment of the apparatus for carrying out the method of the present invention. The apparatus of the second embodiment is different from the apparatus of the first embodiment only in that a metal coating device 6 for forming a metal coating layer on at least one surface of a steel plate is provided in the cooling furnace 5. Be different.

FIG. 3 is a schematic explanatory view showing a third embodiment of the apparatus for carrying out the method of the present invention. In the apparatus of the third embodiment, the metal coating apparatus 6 for forming the metal coating layer on at least one surface of the steel sheet is provided on the outlet side of the soaking furnace 4 only in the first embodiment. Device.

[0042]

EXAMPLES Next, the method of the present invention will be described by way of Examples in comparison with Comparative Examples. (Example 1) 50 of each of the steels A to K having the chemical composition shown in Table 1
T was melted in a converter and then cast into slabs.
Then, the slab was hot-rolled to prepare a hot-rolled steel sheet, the obtained hot-rolled steel sheet was pickled, and then cold-rolled to prepare a cold-rolled steel sheet.

[0043]

[Table 1]

The cold-rolled steel sheets of the steel grades A to K thus prepared were passed through the apparatus shown in FIG. 1 and annealed at a temperature of 850 ° C. in the heating furnace 3 and the soaking furnace 4, and then,
Fe was coated on the surface of the cold-rolled steel sheet with a thickness of 0.1 μm by a metal coating device 6 arranged in the snout 7. In this way, the cold-rolled steel sheet having the Fe coating layer formed on the surface thereof is introduced into the hot dip galvanizing tank 8 and the hot dip galvanizing bath containing 0.13 wt.% Al at a temperature of 460 ° C. A hot-dip galvanized layer was formed on the surface. Then, the steel sheet on which the hot dip galvanized layer is formed is guided to an induction heating system (IH) alloying furnace 10 and heated to a plate temperature of 500 ° C. by the alloying furnace 10 to form an alloyed hot dip galvanized layer, Thus, a specimen of the galvannealed steel sheet shown in Table 2 having an Fe content of about 10 wt.% And a plating amount of 60 g / m ^{2 on} one side of the galvannealed steel sheet (hereinafter referred to as the present invention). No.)
1-11 were prepared.

For comparison, cold-rolled steel sheets of steel types A to K were used for the rewinding machine 1, heating furnace 3, soaking furnace 4, cooling furnace 5, snout 7, hot dip galvanizing shown in FIG. Using a conventional apparatus consisting of tank 8, gas wiper 9 and alloying furnace 10, cold-rolled steel sheet was subjected to hot dip galvanizing treatment and alloying treatment without forming a metal coating layer. Samples of comparative alloyed hot-dip galvanized steel sheets (hereinafter referred to as comparative samples) Nos. 1 to 11 were also shown.

[0046]

[Table 2]

Example 2 By the same method as in Example 1, an alloyed hot-dip galvanized layer was formed on the surface of the cold-rolled steel sheet, and then Fe: 80w was added on the alloyed hot-dip galvanized layer.
Fe-Z in an amount of 5 g / m ^{2 with} a composition of t.% and Zn: 20 wt.%
An n-alloy electroplating layer was formed, and thus, inventive samples Nos. 12 to 22 shown in Table 3 were prepared.

(Example 3) Further, in the metal coating device 6, the surface of the cold-rolled steel sheet was coated with a metal and an alloy other than Fe.
Samples Nos. 23 to 31 of the present invention shown in Table 3 were prepared in the same manner as in Example 1 except that the coating was performed at a thickness of 1 μm. Further, the test samples Nos. 32 to 34 of the present invention shown in Table 3 were prepared in the same manner as in Example 1 except that the heating by the alloying furnace 10 was performed by the gas heating method (GAS).

[0049]

[Table 3]

For comparison, a cold-rolled steel sheet made of steel types A to K was used, as shown in FIG.
Using a conventional apparatus consisting of a heating furnace 3, a soaking furnace 4, a cooling furnace 5, a snout 7, a hot dip galvanizing tank 8, a gas wiper 9 and an alloying furnace 10, in a pre-plating tank 13 for cold rolled steel sheets. Fe was pre-plated and the amount of Fe on the surface of the steel sheet was 5 g / m ^2.
After forming the pre-plated layer, this was annealed, and then subjected to hot dip galvanizing treatment and alloying treatment, thus preparing comparative sample Nos. 12 to 22 shown in Table 4 together.

[0051]

[Table 4]

The metal coating means in the metal coating device 6 for each of the samples of the present invention is as follows. In addition,
The thickness of the formed metal coating layer was determined by the Auger analysis method. Fe coating: Carbon carbonyl iron is supplied with N ₂ gas as a carrier gas by the metal coating device 6 arranged in the snout 7, and Fe is a steel sheet by the reaction of Fe (CO) ₅ → Fe + 5CO by the CVD method. Attached to the surface of. Ni coating: The metal coating device 6 placed in the snout 7 supplies carbonyl nickel using N ₂ gas as a carrier gas, and the CVD method produces Ni (CO) ₄ → Ni + 4CO.
Ni was attached to the surface of the steel sheet by the reaction of.

Co coating: Co was deposited in an alumina crucible as a metal coating device 6 arranged in the snout 7.
It was heated at a temperature of 1660 ° C. and evaporated to adhere to the surface of the steel sheet. Cu coating: Cu was heated at a temperature of 1280 ° C. and evaporated in an alumina crucible as the metal coating device 6 placed in the snout 7 and deposited on the surface of the steel sheet.

Alloy coating: In an alumina crucible as the metal coating device 6 placed in the snout 7, each metal forming the alloy was heated and evaporated by electron beam heating and deposited on the surface of the steel sheet.

Specimen of the present invention prepared as described above
For each of Nos. 1 to 34 and comparative specimens Nos. 1 to 22, plating performance, appearance, powdering resistance and ED paintability were investigated by the performance test described below, and the test results are shown in Table 2. The results are also shown in FIGS.

(1) Platability: The state of occurrence of non-plating was visually inspected and evaluated by the following. ⊚: No plating occurred, very good, ○: Almost no plating, good, Δ: Slight spotless plating, ×: Large spotless plating, Defective, XX: Plating repelling occurred and extremely defective.

(2) Appearance: The state of occurrence of alloying unevenness was visually examined and evaluated by the following. ⊚: Almost no alloying unevenness was generated, which was very good. ○: Almost no alloying unevenness was generated, which was excellent. Δ: Fine streak unevenness was generated. ×: Clear streak unevenness was generated and was poor. X: Clearly large streaks were generated, which was extremely poor.

(3) Powdering resistance: When an adhesive tape was attached to the surface of each specimen, a 90 ° bending test was performed on the specimen with the adhesive tape thus attached, and then the adhesive tape was peeled off. The amount of peeling of the alloyed hot-dip galvanized layer was examined and evaluated by the following. ◯: No peeling occurred in the plating layer, ×: Peeling occurred in the plating layer.

(4) Electrodeposition (ED) coatability: After degreasing the surface of each test piece, chemical conversion treatment was performed using the chemical conversion treatment liquid PB-L3080 (manufactured by Nippon Parkerizing Co., Ltd.), and the surface of each test piece was treated. A chemical conversion coating was formed on top. Then, using paint El-2000 (Kansai Paint Co., Ltd.), this paint was stirred at a temperature of 29 ° C. for 3 days to stabilize it, and then electrodeposition (ED) was performed under the following conditions.
After coating, a coating film with a thickness of 20 μm was formed on the chemical conversion treatment film. Voltage: 280V Bath temperature: 27 ℃ Baking temperature: 170 ℃ Baking time: 25 minutes

The state of crater generation in the coating film thus formed on each test piece was visually inspected,
It was evaluated by the following. ○: No crater was generated ×: Crater was generated

As is apparent from Table 2, the comparative specimens Nos. 1 to 11 obtained by subjecting the cold-rolled steel sheet to the hot dip galvanizing treatment and the alloying treatment without forming the metal coating layer,
All or at least one of plating property, appearance, powdering resistance and ED coating property was poor. Then, the cold-rolled steel sheet shown in Table 4 was pre-plated with Fe on the surface of the steel sheet in a pre-plating tank, annealed, and then hot-dip galvanized and alloyed. Samples Nos. 12 to 22 for use were also inferior in all or at least one of plating property, appearance, powdering resistance and ED coating property.

On the other hand, after cold-rolled steel sheet is annealed, its surface is coated with Fe and other metals, and the steel sheet coated with such metal is subjected to hot dip galvanizing treatment and alloying treatment to form an alloy. Example 1 in which an improved galvanized layer was formed
Inventive specimen Nos. 1 to 11 and Example 3 inventive specimen Nos. 23 to 34 are all excellent in plating property, appearance and powdering resistance except for ED paintability. It was

Then, an alloyed hot-dip galvanized layer was formed on the surface of the cold-rolled steel sheet by the method of the present invention, and then an Fe-Zn alloy electroplated layer was formed on the alloyed hot-dip galvanized layer. The test samples Nos. 12 to 22 of the present invention of Example 2 are
It was excellent in terms of plating properties, appearance, powdering resistance and ED paintability.

FIG. 6 shows that after cold-rolled steel sheet is annealed by the method of the present invention, its surface is coated with metal, and the steel sheet thus coated with metal is subjected to hot dip galvanizing treatment and alloying treatment. Alloyed hot-dip galvanized layer is formed by a conventional method, and the cold-rolled steel sheet is pre-plated with metal in the pre-plating tank in the pre-plating tank, then annealed, and then hot-dip zinc is applied. With the case where the alloying hot-dip galvanized layer is formed by performing the plating treatment and the alloying treatment,
It is a graph which shows the relationship between the thickness of a metal coating layer, and a non-plating score.

In FIG. 6, the method of the present invention is the case of using the specimen of the present invention using the steel types A, B and C shown in Table 1. Conventional methods a, b, and c are conventional methods in which a cold-rolled steel sheet is pre-plated with a predetermined amount of metal or alloy, then annealed, and then hot-dip galvanizing treatment and alloying treatment are performed. Method (a) is for comparative specimens using steel type A, Conventional method (b) is for comparative specimens using steel type B, and Conventional method (c) is for comparative specimens using steel type C This is the case of the specimen. The plating conditions for each specimen are
It is as follows. Annealing temperature: 850 ℃ x 60s Temperature of hot dip galvanizing bath: 460 ℃ Al content in hot dip galvanizing bath: 0.13wt.%

As is apparent from FIG. 6, in the case of the method of the present invention, a coating layer having a very small thickness of 0.01 μm
No non-plating occurred, and the non-plating score was 4, which was very good. On the other hand, in the case of the conventional method (a), about 5
The non-plating score does not reach 4 unless plating with a thickness of μm is applied. In the case of the conventional method (b), the non-plating score is close to 2 even if plating with a thickness of 5 μm is applied. In the case of c), the non-plating score was less than 1 even if plating with a thickness of 5 μm was applied.

[0067]

As described above, according to the present invention,
Forming an alloyed hot dip galvanized layer on the surface of a steel sheet containing elements such as Si, Mn, P, Cu, Ni, Cr, etc. that are more easily oxidized than Fe during annealing or have a strong surface concentration tendency In this case, the galvannealed layer with excellent uniformity and powdering resistance that does not cause non-plating, uneven alloying, etc. can be easily and economically provided without the need to install a large-scale pre-plating facility. An alloyed hot-dip galvanized steel sheet that can be formed and has particularly high strength and excellent corrosion resistance can be efficiently and economically produced, and industrially useful effects are exhibited.

[Brief description of drawings]

1 is a schematic illustration showing a first embodiment of an apparatus for carrying out the method of the present invention.

FIG. 2 is a schematic illustration showing a second embodiment of the apparatus for carrying out the method of the present invention.

FIG. 3 is a schematic explanatory view showing a third embodiment of the apparatus for carrying out the method of the present invention.

FIG. 4 is a schematic explanatory view showing an example of an apparatus of a conventional method.

FIG. 5 is a schematic explanatory view showing another example of the apparatus of the conventional method.

FIG. 6 is a graph showing the relationship between the metal coating layer formed by the method of the present invention and the conventional method and the non-plating score.

[Explanation of symbols]

 1 rewinding machine, 2 steel plate, 3 heating furnace, 4 soaking furnace, 5 cooling furnace, 6 metal coating device, 7 snout, 8 hot dip galvanizing tank, 9 gas wiper, 10 alloying furnace, 11 sink roll, 12 zinc Plating bath, 13 pre-plating bath.

Claims (3)

[Claims] 1. A steel sheet is continuously annealed, and then the annealed steel sheet is continuously passed through a galvanizing bath,
The steel sheet is subjected to a hot dip galvanizing treatment to form a hot dip galvanized layer on at least one surface of the steel sheet, and then the steel sheet having the hot dip galvanized layer formed thereon is heated to undergo an alloying treatment. Thus, in the method for producing an alloyed hot-dip galvanized steel sheet, which comprises forming an alloyed hot-dip galvanized layer on at least one surface of the steel sheet, before passing the annealed steel sheet into the galvanizing bath. And Fe, N on at least one surface of the steel sheet.
Metal coating having a thickness of 0.01 to 3.0 μm on at least one surface of the annealed steel sheet coated with one metal or two or more alloys selected from the group consisting of i, Co and Cu. It is characterized in that a steel sheet on which a layer is formed and a metal coating layer is thus formed is subjected to hot dip galvanizing treatment with a galvanizing bath containing 0.05 to 0.20 wt.% Al, and then subjected to alloying treatment. And a method for producing a galvannealed steel sheet. 2. The method according to claim 1, wherein the alloying treatment of the steel sheet on which the hot-dip galvanized layer is formed is performed by an induction heating type alloying furnace. 3. The steel sheet having an alloyed hot-dip galvanized layer formed on at least one surface of the steel sheet, containing 50 wt.% Or more Fe on the alloyed hot-dip galvanized layer, 1 g /
The method according to claim 1 or 2, wherein the Fe-Zn alloy electroplated layer is formed in an amount of m ² or more.